The use of electronic article security systems for detecting and preventing theft or unauthorized removal of articles or goods from retail establishments and/or other facilities, such as libraries, has become widespread. In general, such security systems employ a label or security tag which is affixed to, associated with, or otherwise secured to an article or item to be protected or its packaging. Security tags may take on many different sizes, shapes, and forms, depending on the particular type of security system in use, the type and size of the article, etc. In general, such security systems are employed for detecting the presence or absence of an active security tag and, thus, a protected article as the security tag and the protected article pass through a security or surveillance zone or pass by or near a security checkpoint or surveillance station.
The security tag which is affixed to or otherwise associated with the article being secured can be implemented with a variety of technologies. More advanced tags allow for single use remote deactivation, single use remote activation, single use remote activation and deactivation, and multiple use remote activation and deactivation.
The security tags which are disclosed herein are tags which are designed to work primarily with radio frequency (RF) electromagnetic field disturbance sensing electronic security systems of the types disclosed in U.S. Pat. Nos. 3,810,147 entitled "Electronic Security System", and 3,863,244 entitled "Electronic Security System Having Improved Noise Discrimination" and their commercially available implementations and counterparts. Such electronic security systems generally establish an electromagnetic field which is provided in a controlled area through which articles must pass in leaving the controlled premises. A resonant tag circuit is attached to each article, and the presence of the tag circuit in the controlled area is sensed by a receiving system to denote the unauthorized removal of an article. The tag circuit is deactivated, detuned or removed by authorized personnel from any article authorized to leave the premises to permit passage of the article through the controlled area without alarm activation.
Removal of the tag can be difficult and time consuming and, in some cases, requires additional removal equipment and/or specialized training. Detuning the security tag by covering it with a special shielding device such as a metallized sticker is also time consuming and inefficient. Furthermore, both of these deactivation methods require the security tag to be identifiable and accessible, which prohibits the use of tags embedded within merchandise at undisclosed locations or tags concealed in or upon the packaging.
Systems are known for the remote electronic deactivation of a resonant tag circuit such that the deactivated tag can remain on an article properly leaving the premises. Electronic deactivation of a resonant security tag involves changing or destroying the detection frequency resonance so that the security tag is no longer detected as an active security tag by the security system. There are many methods available for achieving electronic deactivation. In general, the known methods involve either short circuiting a portion of the resonant circuit or creating an open circuit within some portion of the resonant circuit to either spoil the Q of the circuit or shift the resonant frequency out of the frequency range of the detection system or both.
One such system is shown in U.S. Pat. No. 3,624,631 in which a fusible link in series with an inductor of the resonant circuit is burned out by the application of energy higher than that employed for detection to deactivate the tuned circuit. Another electronic security system shown in U.S. Pat. No. 3,810,147 employs a resonant circuit having two distinct frequencies, one for detection and one for deactivation. A small fusible link is provided in the deactivation circuit which also includes a second capacitor to provide a distinct deactivation resonant frequency.
Deactivateable security tags are also disclosed in U.S. Pat. Nos. 4,498,076 entitled "Resonant Tag and Deactivator for Use in Electronic Security System" and 4,567,473 entitled "Resonant Tag and Deactivator for Use in Electronic Security System". In one embodiment of these deactivateable security tags, deactivation is accomplished by shorting the tag's resonant circuit using a weak link created by forming an indentation in the tag so as to bring more closely together the metallizations of two different parts of the tag's resonant circuit on opposite sides of the tag substrate and thereby allow electrical breakdown at moderate power levels. Such a breakdown can reliably lead to the formation of a permanent (i.e., not spontaneously reversible) short circuit between the two metallizations. The usual embodiment is to have the indentation within the portion of the security tag which is used as the capacitor of the resonant circuit. Deactivateable security tags of the type disclosed in U.S. Pat. Nos. 4,498,076 and 4,567,473 have been shown to be effective and can be conveniently deactivated at a checkout counter or other such location by being momentarily placed above or near a deactivation device which subjects the tag to electromagnetic energy at a power level sufficient to cause one or more components of the security tag's resonant circuit to either short circuit or open, depending upon the detailed structure of the tag.
Each of the deactivateable security tags disclosed in the patents referenced above requires that a predetermined portion of the tag circuit, structure, substrate or some circuit component be weakened in order to establish a specific area for the tag to short circuit or open circuit upon deactivation, and to allow deactivation at moderate to low power levels. Such weakening generally requires one or more additional steps in the manufacturing process, and may also require the introduction of additional components and/or materials. The present invention comprises an improved deactivateable security tag the manufacture of which does not necessitate any additional steps in the manufacturing process nor the introduction of any additional components or materials beyond those which are needed to make a non-deactivateable security tag. The present invention comprises ways of achieving deactivateability by improvements to the metallization patterns created during manufacture, which allow for moderate to low power remote electronic deactivation of the security tag.